Many stringed instruments, and guitars in particular, require periodic tuning to remain playable. Due to the stresses on the strings and the tuning mechanisms imposed during the normal course of use of the instrument, constant tuning may be required, even during the course of a single performance. The need for constant tuning may disrupt the flow of a performance and is a distraction for the musician.
Automatic tuners for guitars are well known in the art. Most are built into a guitar or require major modification to retrofit into a guitar and consist of a sensor for sensing the pitch of a string and a means for tensioning the string to achieve the proper tension.
Such a system is described in U.S. Pat. No. 6,437,226, issued Aug. 20, 2002 to Oudshoorn, et al. The patent describes system wherein a signal is induced onto a string under tension by a linear displacement motor. The resonance signal generated by the string is picked up by a transducer, converted to a digital signal and analyzed by a microprocessor. The motors then tension or slacken the string in response to the analysis to achieve the proper tuning.
Another such system is sold by Tronical, GmbH of Hamburg, Germany. The Tronical system requires that the musician strum the strings of the instrument to generate a test frequency, which is then analyzed by a microprocessor. The strings are tensioned or slackened by machine heads which are driven by servo motors.
Both the Oudshoorn system and the Tronical system are capable of tuning a guitar, regardless of how far out of tune. Such systems, however, not only are expensive, but have the drawback of requiring permanent installation in a guitar. Therefore, it would be desirable to have a device for keeping a stringed instrument in tune that could be used with any instrument, without the requirement of major modification to the guitar for permanent installation.